Traditionally natural cheese is made by developing acidity in milk and setting the milk with a clotting agent, such as rennet, or by developing acidity to the isoelectric point of the casein. The set milk is cut and whey is separated from the curd. The curd may be pressed to provide a cheese block. Curing typically takes place over a lengthy period of time under controlled conditions. Cheddar cheese, for example, is often cured for a number of months, and may be cured for a period in excess of one year, to obtain the full flavor desired.
Numerous reports have been published implicating several compounds to be important in the development of cheese flavor in cheese products. The main classes of compounds thought to contribute to flavor generation in cheese include amino acids, peptides, carbonyl compounds, fatty acids and sulfur compounds. Urbach, G., Contribution of Lactic Acid Bacteria to Flavor Compound Formation in Dairy Products, Int'l Dairy J., 1995, 3:389-422. Several volatile compounds including fatty acids, esters, aldehydes, alcohols, ketones and sulfur compounds are included in lists describing the aroma of various cheeses. Production of several of these aroma and flavor compounds has been attributed to multiple enzymatic and chemical reactions that take place in a sequential manner in ripening cheese.
Various microorganisms have been identified and selected for their ability to produce particular flavors in a cheese ripening environment. These flavors arise through a series of enzymatic steps. For example, in cheese, degradation of proteins by proteases and peptidases can lead to the production of peptides and free amino acids. These precursors are shuttled through subsequent enzymatic and chemical reactions resulting in the formation of flavor compounds. An understanding of these reactions helps in the creation of flavors of a desired cheese type. Fox, P., Cheese: Chemistry, Physics and Microbiology, pp. 389-483, 1993.
Cheese manufacturers are interested in developing cheese products requiring less storage time before they are favorable enough for commercial distribution. Cheese makers have used a wide variety of different techniques in efforts to accelerate the cheese curing or ripening process. Published U.S. patent application Ser. No. US 2001/0024667 A1 provides a summary of a number of these techniques used for accelerating ripening of hard block cheeses, and reference is made thereto.
Another approach used to avoid lengthy cheese ripening periods has been to make a cultured cheese concentrate (“CCC”) having more intense cheese flavor, and then use the CCC in various products to provide cheese flavoring. CCC's which attain full cheese flavor development within a number of days instead of months can be prepared. These CCC's are added to other bulk foods, such as process cheeses or snack foods, to impart or intensify a cheese flavor in them. Methods for the manufacture of such cheese-flavored concentrates have been described, such as in U.S. Pat. No. 4,708,876. Typically the process involves a dairy substrate that is cultured with a lactic culture followed by addition of various proteases, peptidases and lipases. The '876 patent describes cheese flavored concentrates that can be obtained from milk as a starting material, instead of cheese curds, and/or without formation of whey by-product.
However, even if these prior processes may produce an accelerated development, or an enhancement, of cheese flavor, they do not produce enhancements that target specific cheese flavor components. More recently a technology has been developed to produce a natural biogenerated cheese flavoring system that can be used to prepare different cheese products/derivatives, targeted at various cheese flavor profiles using a modular approach to flavor creation, which is described in U.S. Pat. No. 6,406,724. The cheese flavoring system described in the '724 patent is made up of different components, in which the individual components are combined in different ratios to provide specific flavor profiles in the cultured cheese concentrate products.
In addition, the effects of bacteriocin producers, when used as adjunct cultures to thermophilic starters of high aminopeptidase activity, on ripening speed in semihard and hard cheeses has been observed and described in the literature. Oumer, A., et al., “The Effects of Cultivating Lactic Starter Cultures with Bacteriocin-Producing Lactic Acid Bacteria,” J. Food Protection, vol. 64, no. 1, pp. 81-86. The use of a bacteriocin-producing E. faecalis culture in a cheese starter system for making a semi-hard cheese at low pH's (below 5.5) for enhancement of cheese flavor after a relatively long ripening period (viz., 21 to 35 days), has been described by Oumer, A., et al., “Defined Starter System Including a Bacteriocin Producer for the Enhancement of Cheese Flavor,” Biotechn. Techniques, 13: 267-270, 1999. The use of live cultures having high levels of proteolytic enzymes and peptidolytic enzymes to debitter enzyme modified cheeses (EMC's) also has been described, such as in U.S. Pat. No. 6,214,585.
However, in addition to accelerating ripening or flavor development in cheeses, another important consideration in modern cheese making is the inhibition of the growth of spoilage and pathogenic microorganisms in the cheese products. For instance, processed block cheese and processed cheese spreads can be vulnerable to spoilage by germination and growth of bacterial spores that originate in the raw cheese and survive the cooking (melt) process used in their manufacture.
Bacteriocins are generally known as being effective in inhibiting pathogenic and spoilage microorganisms in foods, such as described by Twomey, D. et al., Lantabiotics Produced by Lactic Acid Bacteria: Structure, Function and Applications, Antonie van Leeuwenhoek, 82:15-185, 2002, and Cleveland, J., et al., “Bacteriocins: Safe, Natural Antimicrobials for Food Preservation,” Int'l J. Food Micro., 71 (2001) 1-20. Antimicrobials, such as nisin, lacticin, plantaricin C, and so forth, are generally understood to act on sensitive cells by forming pores in the cytoplasmic membrane. This leads to the dissipation of the proton motive force and release of small intracellular molecules like glutamate and ATP, such as described by Twomey et al. and Cleveland et al., referenced above. This renders the cells permeable but still capable of participating in biochemical processes in its environment. The treatment of cells with surface-active agents to help generate such “leaky” cells, has been described in PCT Int'l Publication No. WO 01/47366 A1.
Nisin, in particular, is a peptide-like antibacterial substance produced by certain strains of the dairy starter organism Lactococcus lactis subsp. lactis (formerly known as Streptococcus lactis). Nisin is a small polypeptide of 34 amino acids, which include the atypical residues lanthionine, β-methyllanthionine, dehydroalanine, and dehydrobutyrine. The first-two mentioned residues close the single sulfur rings that are characteristic of nisin and other structurally related bacteriocins. Variants of nisin are known, including, for example, Nisin A and Nisin Z. Nisin's structure is illustrated, for example, in U.S. Pat. No. 5,527,505 to Yamauchi et al. The highest activity preparations of nisin contain about 40 million IU per gram. A commercial preparation, NISAPLIN®, containing about 1 million IU active nisin per gram is available from Aplin & Barrett Ltd., Trowbridge, England. Nisin has no known toxic effects in humans. It is widely used in a variety of prepared dairy foods. Experimental use in preserving other foods has also been reported. The cultures that produce nisin, being lactic fermentations, generally produce lactate as well.
The possibility that nisin may inhibit Gram positive and Gram negative bacteria when used in conjunction with a chelating agent has been described in U.S. Pat. No. 5,753,614. With respect to cheese products in particular, nisin has been used to inhibit growth and toxin formation of spore-forming spoilage organisms in process cheeses, such as described in U.K. Patent 713,251, and in process cheese spreads, such as described in U.S. Pat. No. 4,584,199. The use of a nisin-producing culture to stabilize a cream cheese composition against the growth of microbiological contaminants therein also has been described in U.S. Pat. No. 6,110,509. In the '509 patent, the cream cheese is made using a fermentation step conducted until a composition inoculated with a nisin-producing microorganism attains a pH in the range of 6.2 to 4, more particularly about 5.5, at which point curds and nisin-containing whey are separated.
Despite the developments described in the above publications, a need still exists for cheese flavoring systems that can develop their flavor and ripen more rapidly, such as within several days, without the formation of byproducts like whey, and inhibiting the growth of objectionable or pathogenic microorganisms in the resulting product. The present invention provides a stabilized cultured cheese concentrate and method for its manufacture that meets these and other desirable needs as well as provides other benefits.